"Compulsory", certainly. I'd prefer "course" (or "course unit") for "asignatura", rather than subject, because that is what it means (in practice you could argue that it amounts to the same thing, but the point is that it's referring to taking a particular course within the programme of study). But "mención" is definitely NOT "mention" in English, except in texts inexpertly translated from Spanish. In English, a mention, special or otherwise, is a grading: a level of distinction in the result. But a "mención" is a pathway within the degree programme leading to a particularly area of the general degree subject being mentioned (hence the name) in the degree title. This is normally called a "specialism" in the UK; in the US the term "specialty" is preferred, and you can also talk about "tagged" degrees, where the specialisation is mentioned in the title. "Emphasis" is pretty much the same thing (see below).

Curiously enough, exactly the same issue arose in a recent question; my answer was not chosen, alas, but I am still convinced it was correct:
http://www.proz.com/kudoz/spanish_to_english/certificates_di...

Actually "focus", the chosen answer there, does express the idea; it's just that universities don't use the term (at least not formally).

It's very important to be clear that we are NOT talking here about a major or concentration (these two terms mean the same thing). A major and a minor are different degree subjects that are combined in a personal degree programme. They can be completely different; I've seen a major in Physics with a minor in Art History for example. But "mención" is quite different; it's an area of a particular degree subject.

"Emphasis" is really a very similar idea to "mención". You can have, for example, a Bachelor of Science in Health Sciences with an emphasis in Gerontology. But it's a US term, not (or rarely) used in the UK, and if you are going into British English you should not use it.

"Specialism" is the usual term for this in British universities. This is from Manchester, for example:

"Our flexible management courses share a common first year before allowing you to focus on your chosen specialism to enhance your career prospects. [...]
Your chosen specialism will be reflected in your degree title e.g. BSc (Hons) Management (Marketing) - however, if you do not wish to specialise, you will graduate in BSc (Hons) Management."
http://www.manchester.ac.uk/study/undergraduate/courses/2015...

The analogy is exact, because in Spain, similarly, you're not obliged to do a "mención"; you can just take the generic degree. But if you do want a mención, a named specialism, certain courses are compulsory, and this is one of them.